Urban%20Design%20to%20Accommodate%20Trees:%20Parking%20lot%20Solutions - PowerPoint PPT Presentation

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Urban%20Design%20to%20Accommodate%20Trees:%20Parking%20lot%20Solutions

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The idea is to create a system that can accommodate tree roots ... The trunk flare lifted and disintegrated the curb (see arrow) as roots expanded in diameter ... – PowerPoint PPT presentation

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Title: Urban%20Design%20to%20Accommodate%20Trees:%20Parking%20lot%20Solutions


1
Urban Design to Accommodate Trees Parking lot
Solutions
  • by Dr. Edward F. Gilman, professor
  • Department of Environmental Horticulture
  • University of Florida, Gainesville

http//hort.ufl.edu/woody/planting
2
Outline of topics
  • Introduction
  • Site evaluation
  • Species selection
  • Formula for success
  • Roots/hardscape conflicts
  • Trees/sidewalk solutions
  • Parking lot/buffer strip solutions
  • Structural soils

3
Solutions for trees in parking lots and buffer
strips
Solutions
  • The idea is to create a system that can
    accommodate tree roots while minimizing
    interference and damage to the infrastructure
  • design and structure
  • edge buffer strips
  • islands
  • interior linear strips

4
Parking lot construction
design
  • Parking lots are carved out of existing soil or
    are developed after soil has been removed or
    added to the area in either case, severe soil
    disturbances almost always occur
  • This makes it tough to grow trees in islands and
    other small soil spaces constructed in the
    parking lot

5
Parking lot design--we can do better
design
  • Parking lots are typically located between the
    street and the building with signs placed on the
    building about 20 feet from the ground

This places tree canopies and signs in immediate
conflict with each other because they occupy the
same vertical space---it is difficult for
customers to view signs and the building
6
Parking lot design--we can do better
design
  • There are many ways to design parking lots
    differently, resulting in more sustainable urban
    areas
  • place signs closer to the ground
  • place signs out by the street and not on the
    building
  • build the parking lot on the back side of the
    building
  • install trees with a dominant single trunk and
    train the lowest branches so they are at least 25
    feet off the ground
  • move the trees to the side of the buildings and
    property borders

7
Signs and trees sharing the same space
design
  • When tree canopies grow in the same space as
    signs, store owners respond by either topping or
    rounding over the trees, or inappropriately
    raising the canopy
  • Raising the canopy on single trunked trees
    results in less maintenance and a longer-lived
    tree than raising the canopy on the multi-trunked
    trees pictured here

Installing trees with one dominant leader and
one trunk in parking lots makes it easier to
remove lower branches as they get in the way of
the signs
8
Sustainable parking lot design
design
  • Trees are located only in the buffer strips
    surrounding this parking lot--no trees are placed
    in islands.
  • This keeps lights away from trees and ensures
    that trees will not have to be pruned to make way
    for the lights
  • Locating trees in large buffer strips around
    the parking lot provides roots with adequate
    space to grow

9
Most trees in buffer strips--one large island
design
  • Trees are located primarily in the buffer strips
    surrounding this parking lot, not in islands
  • There is only one island (left side) and it is
    quite large
  • Large parking lot islands and wide buffer strips
    support large trees

10
Large island supporting trees and shrubs
design
This large island is supporting many trees and
shrubs
  • The parking stalls are located over porous pavers
    that support grass growth
  • This design allows water and air to enter the
    soil and should reduce the amount of water
    running off the parking lot

11
Non-sustainable buffer strips under wires
design
Buffer strips at the edge of parking lots are
often located under utility wires. THIS DOES NOT
WORK!
  • Trees must be pruned to keep them small
  • This makes for unnecessary work and prevents the
    urban forest from developing
  • Move this large soil space from under the wires
    to a different location such as the side of the
    property as in the next slide

12
Sustainable buffer strip on side of property
design
Trees in large soil spaces with no utility lines
nearby can grow to a large size.
  • Buffer strips on the side of the property make
    more sense
  • Often, there are no utility lines on the side of
    the property

13
Porous pavers for parking stalls
design
This parking lot for a large zoo in the southern
U.S. was designed to reduce runoff and support
good tree growth
  • Traditional pavement was used for the travel
    lanes cars stalls were constructed of porous
    paver blocks
  • This should allow for better root growth because
    air and water is more likely to enter the soil
    under the porous pavers

14
Porous pavers near existing trees
design
  • This parking lot for a large botanical garden was
    constructed near existing large trees
  • Porous pavers were used to help preserve the root
    system and soil structure
  • Be sure that the soil grade is not lowered during
    the construction process because this will damage
    roots
  • Soil can be added around the roots to prepare a
    base for the pavers, but be sure it is coarser
    than the existing soil

15
Porous pavers near existing trees-detail
design
  • A close up of the previous photo shows that a
    large portion of the root system was apparently
    protected during construction
  • Be sure soil is not removed from the root zone
    prior to laying the sub-base and the pavers
    because this would remove a large portion of the
    root system
  • This photo shows what happens when some of the
    construction detail was left to chance--note the
    huge damage to the trunk on the tree in the
    foreground

16
Gravel as a parking lot surface
design
  • Gravel has been used successfully for two decades
    in this large employee parking lot
  • Trees are very happy and have grown to form a
    closed canopy
  • If roots grow to the soil surface forming an
    irregular surface, more gravel is added

17
Porous asphalt as a parking surface
design
  • Porous asphalt allows water to run through the
    surface to a layer of gravel below the surface
  • Forty percent of the volume below the surface is
    air space that can fill with runoff water
  • This reduces the volume running into adjacent
    retention ponds and streams

18
Solutions for trees in parking lots and buffer
strips
Solutions
  • The idea is to create a system that can
    accommodate tree roots while minimizing
    interference and damage to the infrastructure
  • design and structure
  • edge buffer strips
  • islands
  • interior linear strips

19
Buffer strip too narrow to sustain trees
Buffer
  • Installation of buffer strips around the edge of
    parking lots are typically mandated by municipal
    ordinances and codes
  • Narrow buffer strips are fine for shrubs but they
    are too small to accommodate root growth needed
    to support trees
  • The large maturing honeylocust trees are likely
    to struggle if roots somehow find suitable soil
    under the walk and pavement, the hardscape is
    likely to become dislodged and damaged

20
Buffer strip too narrow--tree breaks hardscape
Buffer
  • The original space allocated for the tree roots
    was much too narrow
  • Roots somehow found suitable soil under the
    pavement and walk where they grew very well in
    the 20 to 30 years after planting
  • The trunk flare lifted and disintegrated the
    curb (see arrow) as roots expanded in diameter

21
Buffer strip suitable to sustain trees
Buffer
  • The fifteen foot wide buffer strip at the left
    edge of this parking lot is more suitable for
    tree growth than in many designs
  • It will allow for root flare expansion and
    provide open soil for good root growth for a
    decade or two
  • One key to success in this design will be
    preventing compaction by keeping pedestrians off
    the soil and mulch in the strip

22
Buffer strip suitable to sustain trees
Buffer
  • The fifteen foot wide buffer strip between
    building and street is more suitable for tree
    growth than many other designs
  • It will allow for root flare expansion and
    provide open soil for good root growth for a
    decade or two
  • Roots can share soil in the long strip of open
    soil space
  • One key to success in this design will be to
    prevent compaction by keeping pedestrians off the
    soil and mulch in the strip

23
Buffer strip suitable to sustain trees for long
time
Buffer
  • The thirty foot wide buffer strip at the edge of
    the parking lot above is more suitable for tree
    growth than in most other designs
  • That is the reason why these trees have grown so
    large

Large soil space in buffer strips equates to
healthy, vigorous trees
24
Solutions for trees in parking lots and buffer
strips
Solutions
  • The idea is to create a system that can
    accommodate tree roots while minimizing
    interference and damage to the infrastructure
  • design and structure
  • edge buffer strips
  • islands
  • interior linear strips

25
Large trees are not suited for small islands
Islands
  • Planting large-maturing trees in small parking
    lot islands is not sustainable something will
    break
  • Nonetheless we continue to see landscape
    architects specify large-maturing trees for small
    parking lot islands

26
Standard planting in a parking lot island
Islands
  • Here is a group of standard-issue parking lot
    islands, each with two red maple trees
  • The space is too small to sustain tree growth for
    very long
  • Red maple can grow OK in this situation in
    northern climates but struggles in the South

27
Where are the roots?
Islands
  • Occasionally trees can grow in places that seem
    to defy reason.
  • In the parking lot pictured here trees were able
    to explore the soil below the pavement and become
    quite large in relation to the tiny soil space at
    the base of the trunk
  • This example should not be used as a model for
    successful design since it is so atypical

28
Big island means healthier trees
Islands
  • Here is a parking lot constructed on a compacted
    clay soil
  • The two trees on the left and center (blue
    arrows) are larger and darker green than the tree
    on the right
  • The stressed tree on the right was planted in a
    tiny island whereas the healthier ones were in a
    larger island.

29
Small trees for small islands
Islands
  • Small-maturing trees such as crape myrtle are the
    best ones to choose for small islands
  • They cause less damage to hardscape than trees
    that grow to be large

30
Large tree running out of soil space
Islands
  • Large trees planted in small parking lot islands
    may grow well for 20 years when they completely
    fill the soil space with roots, they begin to
    decline
  • This sawtoothed oak grew here for about 20
    years before beginning to show decline as
    indicated by die-back in the canopy (arrows)

31
Large tree growing well in small space
Islands
  • Large trees planted in small parking lot islands
    constructed over certain soil types can explore
    the soil beneath the pavement
  • As roots grow and expand in diameter they often
    begin to lift the curbs and crack the pavement
    (blue arrows)

32
Large tree cracking curb in small space
Islands
  • Large trees planted in small parking lot islands
    constructed over coarser soil types can explore
    the soil beneath the pavement
  • As roots grow and expand in diameter they often
    begin to lift the curbs and crack the pavement

33
Very large tree cracking curb in narrow island
Islands
  • The root system on this tree managed to find a
    way to explore the soil directly under the
    pavement
  • Two large roots can be seen lifting the pavement
    (blue arrows) research shows that water and air
    are abundant on the underside of the pavement
    surface
  • When a tree manages to get large in a small
    space, roots typically destroy hardscape

34
Roots lifting curbing in narrow island
Islands
  • Trees can grow large in small spaces but the hard
    surfaces nearby often suffer serious damage
  • There is no way to replace this curbing back to
    its original location and save the tree

35
Large island with large-maturing oak tree
Islands
  • Designing parking lots with large islands such as
    the one pictured above will allow large-maturing
    trees to be planted with less risk of them
    disrupting hardscape
  • Large diameter buttress roots that can raise
    curbs and walks are farther away from curbs

36
Large islands with large-maturing oak trees
Islands
  • Designing parking lots with large islands such as
    the two pictured here allow large-maturing trees
    to be planted with less fear of them disrupting
    hardscape

37
A peninsula can increase available soil space
Islands
  • Designing parking lots with peninsulas is a good
    method of supplying trees with much more root
    space than the traditional island
  • An island is surrounded on all sides by curbing
  • Recent research shows that the fewer the curbs
    surrounding the tree the better its growth

38
A peninsula can increase available soil space
Islands
  • Trees can grow to be quite large in a peninsula
    because roots have access to ample soil space

39
Solutions for trees in parking lots and buffer
strips
Solutions
  • The idea is to create a system that can
    accommodate tree roots while minimizing
    interference and damage to the infrastructure
  • design and structure
  • edge buffer strips
  • islands
  • interior linear strips

40
Linear planting strips in a parking lot
Linear strips
  • Trees can grow very well in long planting strips
    in parking lots
  • Combined with the traditional island at the end
    of the strip as shown above, this design can lead
    to many shaded parking spaces. Security lights
    will conflict (arrow)

41
Linear planting strips can conflict with signs
Linear strips
  • Trees in long strips can conflict with building
    signs if the site is not designed correctly
  • In this design, the security lights (blue arrow)
    are located away from the tree planting strips
    this eliminates conflicts between lights and
    trees and reduces maintenance

See next slide for alternatives
42
Alternatives to tradition
Linear strips
  • move the trees to the edge and sides of the
    property
  • select and train trees to a single leader to ease
    canopy raising
  • reduce sign height
  • move the signs to the front edge of the property
  • move the building toward the street and place
    trees behind building

43
Linear planting strips supporting trees
Linear strips
  • These trees in a long, fairly wide planting strip
    are growing well
  • The close spacing between trees allowed the
    canopy to close quickly over the parking spaces

44
Long strips support healthy trees
Linear strips
  • These three trees in a long planting strip are
    growing well
  • The shrubs and ground cover planted in the strip
    help keep people off the soil, thereby preventing
    soil compaction
  • Compacted soil can dramatically reduce tree growth

45
Trees are growing into lights
Linear strips
  • These trees are growing nicely due to good site
    design long linear strips allow roots to share
    soil space
  • However, since the security lights were installed
    way too high (blue arrows) the tree canopy is
    beginning to reach the lights
  • This conflict often leads to poor tree pruning
    choices resulting in unhealthy trees

46
Trees healthy due to lots of soil space
Linear strips
  • These trees are growing nicely due to good site
    design
  • Long linear strips allow roots to share soil space

47
Success from long linear soil strip
Linear strips
  • Long wide strips are better able to support trees
    than small islands
  • Here is a very successful project using clonal
    trees that created a nice border and screen

48
Wider is better
Linear strips
  • Very wide soil strips in parking lots allow for
    optimal tree growth
  • This strip is forty feet across and will
    support trees for decades

49
Wide strip supporting a double tree row
Linear strips
  • Very wide soil strips in parking lots provide the
    best trees
  • This strip is fifty feet across and has supported
    this double row of oaks for decades
  • This is sustainable urban design

50
Root barriers can deflect roots
Solutions
  • Barriers have been placed vertically in the soil
    to deflect roots away from hardscapes
  • Place the barriers sufficiently away from the
    structure (about six inches) to be protected so
    that as the roots grow wider they will not touch
    the curb or walk
  • Be sure the top of the barriers reaches above the
    top of the soil so roots do not grow over it

51
Root barriers can deflect roots
Solutions
  • Roots are deflected horizontally and down by most
    of the barriers on the market
  • In compacted soils and soils with a high water
    table, roots grow under the barrier and up the
    other side
  • In well drained soil, roots may remain at deeper
    depths longer

52
Outline of topics
  • Introduction
  • Site evaluation
  • Species selection
  • Formula for success
  • Roots/hardscape conflicts
  • Trees/sidewalk solutions
  • Parking lot/buffer strip solutions
  • Structural soils

53
Many tools at your disposal
  • Other professionals engineers, planners,
    architects, landscape architects, urban
    foresters, arborists
  • Species selection and spacing
  • Creative design solutions
  • Ordinance and code changes

54
Root barriers can deflect roots
Solutions
  • Barriers have been placed vertically in the soil
    to deflect roots away from hardscapes
  • Place the barriers sufficiently away from the
    structure (about six inches) to be protected so
    that as the roots grow wider they will not touch
    the curb or walk
  • Be sure the top of the barriers reaches above the
    top of the soil so roots do not grow over it

55
Root barriers can deflect roots
Solutions
  • Roots are deflected horizontally and down by most
    of the barriers on the market
  • In compacted soils and soils with a high water
    table, roots grow under the barrier and up the
    other side
  • In well drained soil, roots may remain at deeper
    depths longer

56
Outline of topics
  • Introduction
  • Site evaluation
  • Species selection
  • Formula for success
  • Roots/hardscape conflicts
  • Trees/sidewalk solutions
  • Parking lot/buffer strip solutions
  • Structural soils

57
Typical root growth under pavement
Structural soil
  • Roots (blue arrow) typically grow directly under
    the sidewalk slab as shown here because that is
    where air and moisture is present
  • The sidewalk slab has been remove in the photo
  • Roots lift the walk as they increase in diameter

Photo credit Jason Grabosky, Rutgers University
58
Structural soil design
Structural soil
  • Structural soil is designed to support the weight
    of walks, roads, pedestrians and vehicles as well
    as provide a well-aerated soil substrate for tree
    root growth
  • Weight is transferred from aggregate to aggregate
    then to the soil under the aggregate no weight
    is borne by the soil between aggregates.

Illustration credit Jason Grabosky, Rutgers
University
  • This allows roots to grow well in the soil
    between the aggregates

59
Structural soil installed
Structural soil
  • Structural soil is composed of small aggregate
    material (angular rocks about one inch diameter)
    with enough soil to almost fill the space between
    the rocks

Photo credit Jason Grabosky, Rutgers University
60
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61
Root growth in structural soil after three years
Structural soil
  • Roots grew well in structural soil under a
    sidewalk (walk has been removed-blue arrow) in
    the first three years after planting
  • Roots grew down and out from the tree
  • It is not known if all trees will grow like this
    one

Photo credit Jason Grabosky, Rutgers University
62
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67
Tree growth in structural soil
Structural soil
  • These trees were planted into a strip of
    structural soil installed in this retrofitted
    parking lot between the blue arrows
  • They have performed quite well

Photo credit Jason Grabosky, Rutgers University
68
Tree growth in clay vs. structural soil
Structural soil
  • Trees on the left were planted in clay soil that
    was fairly compacted-typical of many job sites
    many of these trees were performing poorly as
    indicated by the die-back (blue arrow)
  • Trees on the right were planted in structural
    soil installed beneath the sidewalk and they
    looked great

Photo credit Jason Grabosky, Rutgers University
69
Tree growth in well-drained good soil vs.
structural soil
Structural soil
  • Trees on the left were planted in well-drained
    good soil while those on the right were in a type
    of structural soil
  • All trees were planted at the same time

Photo credit Jason Grabosky, Rutgers University
70
Tree growth in well-drained good vs. structural
soil
Structural soil
  • This is a photo of the same site as shown in the
    previous slide about ten years later
  • Canopies have closed to form a nice shaded
    sidewalk
  • Although trees on the right are growing slower
    than those planted in soil, all have grown
    acceptably and none have been replaced

71
Tree in structural soil around parking lot island
Structural soil
  • Structural soil was placed in this parking lot
    island and under the pavement around it
  • Roots should grow under the pavement without
    difficulty because they will be growing in the
    uncompacted soil that is between the aggregates
  • This is likely to allow the tree to grow to a
    large size and provide more benefits to the site
    than a tree that remains small and unhealthy

72
Many tools at your disposal
  • Other professionals engineers, planners,
    architects, landscape architects, urban
    foresters, arborists
  • Species selection and spacing
  • Creative design solutions
  • Ordinance and code changes

73
Urban Design to Accommodate Trees Parking lot
Solutions
  • by Dr. Edward F. Gilman, professor
  • Department of Environmental Horticulture
  • University of Florida, Gainesville

http//hort.ufl.edu/woody/planting
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